A so-called carbon shaft has been known as a golf club shaft. A sheet winding process has been known as a method for manufacturing the carbon shaft. In the sheet winding process, a laminated constitution is obtained by winding a prepreg around a mandrel.
The prepreg includes a resin and a fiber. Many types of prepregs exist. A plurality of prepregs having different resin contents have been known. In the present application, the prepreg is also referred to as a prepreg sheet or a sheet.
In the sheet winding process, the type of a sheet, the disposal of the sheet, and the orientation of a fiber can be selected.
A shaft having a reinforced layer disposed on a thin diameter side portion is disclosed in Japanese Patent No. 3317619. The elastic modulus of a carbon fiber contained in the reinforced layer is 5 to 150 GPa.
A shaft including a middle elastic high strength carbon fiber reinforced resin sheet and a low elastic carbon fiber reinforced resin sheet to reinforce the TIP side of the shaft is disclosed in Japanese Patent Application Laid-Open No. 2004-81230. The reinforcing fiber of the low elastic carbon fiber reinforced resin sheet has a tensile elastic modulus of 5 to 10 ton/mm2 and a compressive breaking strain of equal to or greater than 2.0%. The low elastic carbon fiber reinforced resin sheet is disposed on the outer layer side of the middle elastic high strength carbon fiber reinforced resin sheet.
In Japanese Patent No. 4157357, a composite prepreg having a PAN based carbon fiber and a pitch based low elastic fiber is used. In the composite prepreg, the elastic modulus of the PAN based carbon fiber is 200 GPa or greater and 500 GPa or less, and the elastic modulus of the pitch based low elastic fiber is 45 GPa or greater and 160 GPa or less.
Japanese Patent Application Laid-Open No. 10-329247 discloses a tubular body including an inner layer and an outer layer laminated outside the inner layer. The inner layer includes a reinforcing fiber and a resin. The outer layer includes a glass fiber and a resin. The ratio of the thickness of the outer layer to the total thickness of the tubular body is 5 to 35%.